Automatic test equipment (ATE) refers to an automated, usually computer-driven, approach to testing devices, such as semiconductors, electronic circuits, and printed circuit board assemblies. A parametric measurement unit (PMU) is typically part of an ATE. A PMU is used during device testing to measure parameters, such as voltage and current, at a device pin, and to regulate those parameters. The PMU attempts to ensure that, during testing, proper parameter values are applied to the device under test (DUT). Signals to and from the PMU are typically DC (direct current).
A PMU typically includes circuitry for forcing a voltage and/or current to the DUT. Impedance (e.g., resistance) in a circuit path leading from this circuitry to the DUT affects the amount of current provided to the DUT. This resistance can be calibrated in order to control the current to the DUT. Heretofore, switches were used to switch between an AC (alternating current) calibration and calibration (i.e., DC calibration) associated with the PMU. One problem with this approach is that the switches introduce discontinuities and parasities that corrupt high-speed AC waveforms.